The invention relates to the charging and discharging of storage batteries. It is particularly concerned with a device which continuously monitors the state of charge in terms of the quantities of electrical energy charged and discharged.
An object and feature of the invention is a device which is characterized in that it comprises:
a current sensing resistor connected in series with the battery, the voltage across the said resistor being referred to hereinafter as the input voltage;
at least one chopper amplifier stage providing an amplified voltage with an absolute value proportional to said input voltage;
a voltage to frequency converter providing a train of pulses at a frequency proportional to the absolute value of said amplified voltage; and
a counter responsive to said pulses and to the polarity of the input voltage, the counter being incremented or decremented by said pulses in accordance with the polarity of said input voltage, the state of a logic output of the counter being representative of the state of charge of the battery.
The counter is more accurate and reliable than devices using current integration. In combination with the chopper amplifier stage, it also increases the dynamic range of the battery discharge currents that can be measured. The counter can record very high frequency pulses, corresponding to very high discharge currents, while the chopper amplifier stage eliminates background noise and enables very small discharge currents to be detected.